1. Field of the Invention
The present invention relates to a circular saw in which a work piece placed on the saw's base is cut by a rotary circular saw blade, and more particularly, to improvements in a dust collector for use in such circular saws.
2. Description of the Related Art
A typical circular saw includes a base on which a work piece is set and a vertically pivotable saw assembly including a rotary circular saw blade normally urged upward by a spring. The circular saw further includes an arm mounted on the base and supporting the saw assembly, and a dust collection passage generally defined by a through-hole or a nozzle portion provided in the arm of the saw assembly. The dust collection passage, typically having an opening directed toward the cutting edge of the saw blade, collects dust, chips, and other debris blown toward the arm by airflow caused by the rotating circular saw blade and guides such debris for collecting and subsequent trapping and/or discharge at the rear of the saw assembly. With this arrangement, dust and other debris, typically generated from cut work pieces, is not scattered across the base. By configuring the opening of the dust collection passage in a flared, horn-like shape, dust can be caught efficiently in most cases even when the direction in which the dust travels changes as the saw blade cuts deeper into a work piece during cutting operation.
However, while the above-described example usually works adequately, there are several noticeable deficiencies which have not been solved by conventional dust collection arrangements. One area of deficiency relates to the manner in which the dust collection passage with a flared opening is designed; since the dust collection passage is increasingly narrower toward the exhaust outlet thereof (i.e., its cross sectional area decreases towards the exhaust outlet), the air pressure near the outlet of the passage is higher, often causing turbulence at the narrower portion. This may in turn cause some dust to adhere to the inner wall of the dust collection passage, or in the worst case, creates a counter flow of air, and hence dust, to the opening, thereby lowering the dust collecting efficiency.
Another area of deficiency is related to the smooth operation of the above-described spring, which is typically made of a compression or torsion spring. Since this spring has been connected to a supporting shaft or to the arm with no protection against dust, dust or chips tend to become caught in the gaps in the exposed spring, adversely affecting the operation of the spring and/or the smooth vertical movement of the saw assembly.